The Diameters of Globular Clusters.

Estimates Of the limiting diameters of sixty-nine globular clusters were made on two homogeneous series of Crossley plates, taken inblue and red light. Surface-brightness profiles and diameters at which the surface brightness falls to one-half or to one-ñfth of that at the center were determined for sixty-four clusters. Diameters were determined for circles which would contain the total light of each cluster if the surface brightness were uniformly that of the center of the cluster. For the estimated limiting diameters of clusters known to be free of interstellar absorption, a loose linear relation was found between the absolute magnitude and the logarithm of the linear diameter. The slope of the correlation line is approximately that to be expected if the clusters all have the same average light-density: -M = 7.5 log D + constant

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